The present invention relates to a method for the switching of a number of battery cells in a battery which is configured as an electrochemical storage device. The invention also relates to a battery system with a battery configured as an electrochemical storage device, comprising a number of battery cell units, each comprised of a battery cell and a battery cell monitoring module associated with the battery cell.
FIG. 1 shows a battery system 10 which is known from the prior art, comprising a battery 11 with a number of battery cell units (Smart Cell Units SCU) 20, each comprised of a battery cell 21 and a battery cell monitoring module (battery cell electronic module or battery cell electronics) 22 associated with said battery cell 21. In the interests of simplicity, only two battery cell units are represented in FIG. 1, each of which is designated by the reference number 20. The battery cell monitoring modules 22 permit the individual control of the individual battery cells 21. For the generation of an output voltage (total output voltage) U from the battery 11, which also serves as the output voltage U of the battery system 10, the battery cell monitoring modules 22 are mutually interconnected in series by means of a connecting link. The battery system 10 also comprises a central control unit (CCU) 30 for the control of the battery system 10.
For the generation of a controlled output voltage (total output voltage) U from the battery 11, individual battery cells 21 are brought in-circuit by means of their associated battery cell monitoring module 22, i.e. the battery cells 21 are connected either with a positive or a negative polarity relative to the tap-off of the output voltage U in the series circuit. For the generation of a controlled output voltage (total output voltage) U from the battery 11, individual battery cells 21 are also disconnected by means of their associated battery cell monitoring module 22, i.e. the battery cells 21 to be disconnected are isolated from the series circuit, whereby the connecting terminals of each battery cell 21 to be disconnected by means of the associated battery cell monitoring module 22 are electrically connected, such that the corresponding battery cells 21 are bridged. Consequently, the battery cells 21 connected on the series circuit may each be in a circuit state which is designated as “positively connected” or in a further circuit state which is designated as “negatively connected”. In addition, the battery cells 21 which are isolated from the series circuit are in a circuit state which is designated as “bridged”.
In battery systems 10 of this type (smart cell battery systems), decisions concerning the switchover of the circuit state of the battery cells 21 proceed on a decentralized basis in the respective battery cell monitoring modules 22. Actual control functions are implemented by the central control unit 30, which is configured as a central controller of limited complexity.
To this end, in the battery system 10, a setting for a first control variable P1 and a second control variable P2 is delivered via a communication link 31 which is configured as a unidirectional communication interface via which, from the central control unit 30, only a single message incorporating the current control variables P1 and P2 is transmitted to all the battery cell monitoring modules 22. All the battery cell monitoring modules 22 receive the same message, and either connect their associated battery cells 21 independently to the series circuit, or effect the bridging of their associated battery cells 21 by means of the corresponding switches (not represented) in each battery cell monitoring module 22. In accordance with a control algorithm, the central control unit 30 generates the two control variables P1, P2 in the form of two numerical values which lie between 0 and 1, which are transmitted via the communication link 31 from the central control unit (CCU) 30 to the battery cell monitoring modules (SCU) 22 and received uniformly by all the battery cell monitoring modules 22. The following relationship applies: 0≤P1≤1 and 0≤P2≤1.
In each battery cell monitoring module 22, a uniformly-distributed random process is executed, whereby P1 is interpreted as a first probability to the effect that each disconnected battery cell 21 will be connected, designated as a connection probability, and P2 is interpreted as a second probability to the effect that each connected battery cell 21 will be disconnected, designated as a disconnection probability. The central control unit 30 regulates the control variables P1 and P2 such that the difference (control margin) between a current output voltage U and a desired output voltage Us of the battery system 10 is as small as possible.
In addition, for the generation of a controlled output voltage U from the battery 11, a simple extension of the control algorithm executed by the central control unit 30 may be implemented such that active battery cell function state balancing (battery cell balancing) is achieved by the simultaneous application of a weighted service life for the battery cells 21.
For the generation of a controlled output voltage U from the battery, each battery cell monitoring module 22 scales the relevant control variable P1 or P2, i.e. the identically received control variable P1 or P2, selected in accordance with the circuit state of the associated battery cell 21, is subject to the application of a performance factor, which is calculated with reference to a state of charge (SOC) and a state of health (SOH) of the associated battery cell 21. As a result, for the generation of a controlled output voltage U from the battery during a discharging process, disconnected battery cells 21 with a higher performance factor have a higher probability of being connected than battery cells 21 with a lower (inferior) performance factor and, conversely, battery cells 21 with a lower performance factor have a higher probability of being disconnected than battery cells 21 with a higher performance factor. For the generation of a controlled output voltage U from the battery, as an average over time, battery cells 21 with a lower performance factor are discharged less frequently, thereby permitting the achievement of an active battery cell function state balancing function for the battery cells 21.